This invention relates to a film type solar battery comprising a plurality of series-connected photoelectric conversion elements formed on a translucent insulated substrate.
Non-crystalline or amorphous silicon (hereinafter referred to as "a--Si") is formed by subjecting silane gas to glow discharge decomposition. Because a--Si grows in the gaseous phase, it theoretically can readily have a large area. It is hoped that non-crystalline silicon can be developed as a high output element in a solar battery.
In order to efficiently use the electric power generated by a solar battery, it is desirable that the structure of the solar battery be as shown in FIG. 2, for example, where unitary cells are connected in series to one another. In a solar battery of the type shown in FIG. 2, strip-shaped transparent electrodes 21, 22, 23, 24 and so on are formed on a translucent insulated substrate 1 such as a glass substrate. For example, an ITO (indium tin oxide) film, SnO.sub.2 (tin oxide) film, or ITO/SnO.sub.2 compound film is formed on the entire upper surface of the glass substrate 1 by electron beam vacuum deposition, sputtering, or thermal chemical vapor deposition (CVD), and the film thus formed is subjected to optical etching to form the strip-shaped transparent electrodes 21, 22, 23, 24 and so on. In the same manner, a--Si layers 31, 32, 33, 34 and so forth and metal electrodes 41, 42, 43, 44 and so forth are formed. In order to electrically connect the transparent electrode layers to the metal electrode layers, the metal electrode 41 is brought into contact with transparent electrode layer 22, the metal electrode 42 is brought into contact with the transparent electrode layer 23 and the metal electrode 43 is brought into contact with the transparent electrode layer 24, and so on until all the corresponding metal electrodes are brought into contact with their corresponding transparent electrode layer. Each of the a--Si layers 31, 32, 33, 34 and so on consists of a p-layer of about 100 .ANG. in thickness, a non-doped (i) layer 0.5 um in thickness, and an n-layer of about 500 .ANG. in thickness which are laid one on another in the stated order as viewed from the side of the transparent electrode.
However, the manufacture of the above-described series connection type solar battery of the prior art suffers from the following difficulties:
(1) Pinholes are liable to be formed because of defects in photo-resist layers, thus decreasing the output power of the solar battery;
(2) A chemical treatment is carried out for every film formation, which contaminates the interfaces of the films, thus lowering the output power of the solar battery; and
(3) The manufacturing processes are intricate, and thus the manufacturing cost is increased as the area of the solar battery increases.
In order to eliminate the above-described difficulties, a method has recently been proposed in the art in which the energy of a laser beam is utilized to cut the transparent electrode layer, the a--Si layer and the metal electrode layer into pieces.
Additionally, the present inventors have described a method in Japanese Patent Application No. 213736/1984 in which the a--Si layer is not cut, but instead electrically conductive polycrystalline regions are formed in the a--Si layer by utilizing the energy of a laser beam so that the transparent electrode layer of any one of the photoelectric conversion elements is connected to the metal electrode layer of the next photoelectric conversion element. However, as is described in the specification of the above mentioned patent application, there are several cases where the applied laser beam is either not absorbed or is excessively absorbed. For example, in both cases where the laser beam is applied to the a--Si layer through the metal electrode layer or applied directly to the a--Si layer before the metal electrode layer is formed, a non-uniform thickness in either the a--Si layer or the metal electrode layer causes reflection of the beam to fluctuate. This results in the laser beam being reflected by the layer or passed through it in an unpredictable manner. As a result, the energy necessary for forming polycrystalline regions in the a--Si layer is not absorbed therein, or, in the alternative, the energy of the laser beam is excessively absorbed therein, so that the a--Si layer may be cut and the transparent electrode layer may also be cut. The problems associated with over or under absorption of light are evident. When the a--Si layer is not made polycrystalline, it is so high in resistance that the metal electrode layer on the a--Si layer is not electrically connected to the transparent electrode layer. If the transparent electrode layer is also cut, the electrical connection cannot be obtained. Even if the metal electrode layer is formed later so that the gap formed by cutting of the transparent electrode layer is filled with metal, the metal layer in the gap is brought into contact only with the cross-sectional areas of the transparent electrode layer. The resulting contact area is extremely small such that it is impossible for the metal electrode layer to sufficiently electrically contact the transparent electrode layer. Accordingly, it is necessary for the prior art to monitor and adjust the laser output according to the conditions of the layers, which lowers the manufacturing efficiency in the mass production of solar batteries.